Improving Keystream Generation for Sosemanuk Stream Cipher Using Twofish Block Cipher


This paper will introduce two proposal algorithms (Snowfish 1) and the(Snowfish 2) to improve the Sosemanuk stream cipher algorithm by benefiting fromthe efficient properties of the Twofish block cipher and also use its key schedule, keydependentSbox to increase the security, randomness and try to avoid the guess anddetermine attack of Sosemanuk. These two proposals use Twofish algorithm ratherthan Serpent algorithm which was used in the Sosemanuk and also they use keydependentSbox rather than static Sbox. They are similar in the same key length (128to 256 bit), IV length (128 bit), LFSR length, FSM functions and outputtransformation.In this paper will make a comparison between Snowfish 1, Snowfish 2 andSosemanuk algorithms by using the tests of randomness, the structural tests and thecomplexity of the algorithm. These tests give results that show the two proposedalgorithms have good results in increasing the security and randomness comparedwith Sosemanuk algorithm.